The subject matter relates to an internal voltage generating circuit of a memory device, and more particularly, to a bandgap reference generating circuit for generating a reference voltage or current which is used inside a memory device.
Semiconductor memory devices are used in various fields. Typically, semiconductor memory devices are used to store a variety of data. Semiconductor memory devices are required to have a high capacity, a high operating speed, a small size, and a low power consumption for use in various portable devices, such as desktop computers or notebook computers.
One solution for designing a low-power semiconductor memory device is to minimize a current consumption in a core area of a memory. Memory cells, bit lines, and word lines are provided in the core area, and the core area is designed according to an ultra-fine design rule. Therefore, a power supply voltage should be reduced in order to design an ultra-fine semiconductor memory device that performs a high frequency operation. At present, a power supply voltage lower than 1.5 V is used.
Using an external power supply voltage, the semiconductor device generates various levels of internal voltages. In particular, a semiconductor memory device such as a DRAM generates a core voltage (VCORE), which is used in a core area, a high voltage (VPP), which is higher than the external power supply voltage (VDD) and applied to a gate of a cell transistor, that is, a word line, and a back bias voltage (VBB), which is lower than a ground voltage (VSS) and used for a bulk of a cell transistor.
In order to generate the above internal voltages, a charge-pumping scheme (for VBB and VPP) and a down-converting scheme (for VCORE) are conventionally used. Alternatively, an internal reference voltage (VREF) is primarily generated and then internal voltages (VBB, VPP, VCORE) are secondarily generated using the internal reference voltage (VREF).
The internal reference voltage should have a constant level at a low operating voltage, regardless of process, voltage and temperature (PVT) variations.
In the semiconductor device, a conventional bandgap reference generating circuit for generating an internal reference voltage generates an internal reference voltage that satisfies Zero TC by feeding back an output voltage generated using an amp. Zero TC means that an output voltage is not varied with respect to temperature change. Also, the conventional bandgap reference generating circuit increases a band width in order to improve performance of the amp. At this point, a power supply rejection ratio (PSRR) proportional to the bandwidth is also improved.
However, as the bandwidth is increased in order to improve performance of the amp, the current consumption of the amp increases, which frustrates the low power requirement and energy reduction sought in a low-power semiconductor memory device.
In a normal mode where the semiconductor memory device performs data read/write operations, the current consumption of the amp in the bandgap reference voltage generating circuit does not matter because it is several mA or less. However, in a mode requiring reduced power (a self refresh mode, a low-power mode), the current consumption generated for the increased bandwidth of the amp cannot be ignored.